Load transfer switch mechanism



April 1966 R. G. RUSSELL 3,246,100

LOAD TRANSFER SWITCH MECHANISM Filed Dec. 5, 1962 2 Sheets-Sheet l I 2INVENTOR.

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ATTOR N EYS April 6 R. G. RUSSELL 3,246,100

LOAD TRANSFER SWITCH MECHANISM Filed Dec. 5, 1962 2 Sheets-Sheet 2 BY25/ MVENTOR. FIG.4 7f% ATTO RN EYS United States Patent Oflice 3,246,100Patented Apr. 12, 1966 3,246,100 LOAD TRANSFER SWITCH MECHANESM RaymondG. Russell, Scituate, Mass. (211 Northern Ave., Boston, Mass.) FiledDec. 5, 1962, Ser. No. 242,444 11 Claims. (Cl. 20092) The presentinvention relates to a transfer switch mechanism and more particularlyto a mechanism for automatically transferring an electrical load from apreferred power source to an emergency power source when the preferredpower source fails. 1

An object of the present invention is to provide an improved transferswitch for A.C. or DC. systems which functions to transfer an electricalload from a preferred power source to an emergency source when normalvoltage fails or is significantly reduced below accepted limits and thento restore the load to its original preferred source automatically whenthe preferred power source is restored to a desired level.

Another object of the present invention is to provide a transfer switchmechanism of the type described which is rugged in design and isreliable in operation.

It is also an object of the present invention to provide a design whichis capable of embodying transfer mechanisms having high in-rush andthermal capacities and in which arcing may be minimized. A furtherobject of the present invention is to provide a mechanism which isadapted to either motor or manual operation.

Switching time in transfer switches of the type described is critical inmany applications where continuity of power is essential. The transferof power from a preferred to an emergency source must be substantiallyinstantaneous, not only to minimize power interruption but also tominimize damage to the contacts in that the mechanism due to arcingwhich occurs in slow transfer mechanisms. It is therefore also an objectof this invention to provide high speed transfer mechanism whereinswitching may be elfected between a high power preferred source and anemergency high power source in less than 3 cycles in a 60 cycle system.

A further object of this invention is to provide a transfer mechanismwherein closed contacts are positively locked closed to preventinadvertent opening due to strong stray magnetic fields whichoccasionally have a tendency to open such contacts.

A further object of the invention is to provide a transfer mechanismwherein the preferred and emergency power source terminals are arrangedin tandem in such a manner as to prevent inadvertent short circuitingfrom one power source to the other, and wherein the contact mechanismcannot lock inadvertently into a neutral position.

A further object of the present invent-ion is to provide a transfermechanism wherein substantial kinetic actuating energy is created in theform of spring loading just prior to the actuation of the switchingmechanism whereby the actual switch-ing action takes place at a speedmore rapid than heretofore possible.

The present invention attains these and other objects by providing animproved switching mechanism of the type described wherein the switchingmechanisms for transferring an electrical load from a preferred powersupply to an emergency power supply or vice versa is arranged in tandempairs, with each tandem mechanically interlocked to prevent theswitching mechanisms in the tandem pair from assuming the same closed oropen positions. Also provided is a structure wherein mechanicallyinterlocked tandem pairs of switching mechanisms are actuated by a powersource symmetrical with the tandem pairs. Such arrangement includes agear motor functioning through a crank and interlocked link arrangementto actuate the switching mechanisms of the tandem pairs in phaseopposition. The crank and link arrangement is designed in conjunctionwith the switchinng mechanism to preload the switching mechanism througha spring link means whereby spring elements within each of the switchmechanism functions when actuated, to cooperatively move the contactarms with a positive force. This cooperative movement is in partattained through the mechanical interlock of the contact arms in thetandem pairs.

These objects and advantages of the present invention will be moreclearly understood when considered in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a plan view of a preferred embodiment of the present inventionillustrating a 3-pole switch,

FIGS. 2 and 3 represent schematic elevations of the switch shown in FIG.1 respectively in two different positions of operation; and

FIG. 4 is a schematic view of the circuitry associated with themechanism.

While the present invention will be described in conjunction with a3-p0le switch, it should be understood thta the principles hereindisclosed are applicable to single or other multiple pole switches. Theconstruction is also susceptible to various modifications, adaptationsand other uses. Moreover, it may be actuated manually or automaticallyas described. In its preferred form the present invention is useful fortransferring a load from a normal or preferred powered source to anemergency source automatically, on the occasion of a partial or completefailure of the preferred power source and an automatic return to thepreferred power source to its desired level.

Referring to FIG. 1 there is illustrated a transfer switch mechanismwhich may be mounted on a suitable switchboard 12, having associatedcircuitry, described later in connection with FIG. 4, for operating thetransfer switch mechanism of the present invention. In the embodimentillustrated three circuit breakers or switching mechanisms 13, 14 and15, each having terminals 13A, 14A and 15A for connection to normal orpreferred powered sources are secured to the switch-board 12. Circuitbreakers or switch mechanism 16, 17 and 18 each having terminals 16A,17A and 13A for connections to an emergency power source are alsosecured to the switchboard 12. The individual circuit breakers in thefirst group of switch mechanisms are arranged in parallel or tandem withindividual circuit breakers in the second group of switch mechanisms.Thus circuit breakers 13 and 16; 14 and 17; and 15 and 18; are arrangedin parallel or tandem pairs.

These circuit breakers are preferably constructed with an over-centerspring actuated toggle action best illustrated schematically in FIGS. 2and 3. The construction of these circuit breakers, which will bedescribed specifically in connection with the circuit breaker 14 whichapplies to each of the circuit breaker mechanisms, is one which ispresently commercially available. These circuit breakers each areprovided with contact terminals 14A adapted to receive a power supplyload. This terminal 14A is electrically connected to a fixed contact 24.A contact arm 20 is pivotally supported at one end 21 to allow themoveable contact 22 to pivot into and out of engagement with the fixedcontact 24. The contact arm 20 is actuated through a toggle mechanism28. This toggle mechanism comprises links 26 and 27 pivotallyinterengaged at adjacent ends 29. One end of the toggle mechanism 28 ispivotally interengaged with the contact arm 20 intermediate its ends at30, and the other end of the toggle mechanism is pivotally secured to afixed member 31. In actual commercial embodiments the member 31 maycomprise a frame pivotally secured for limited movement to a basesupport such as base support 35. The toggle mechanism is actuated by alever 34 pivotally supported on a fixed support 35 at one end 36, withits other end interengaged with the interconnected ends 29 of the links26 and 27 by the spring link 39. In actual commercial embodiments a pairof springs are used one on either side of the toggle and are eachconnected to lever 34 by a connecting pin.

These circuit breakers have a bi-stable condition with the two positionsillustrated at the right ends respectively of FIGS. 2 and 3. Thecondition illustrated at the right end of FIG. 2 is a normal conditionwhile that illustrated in FIG. 3 is an alternate or emergency condition.When the lever 34 moves in a clockwise direction from the positionillustrated in FIG. 2, to that illustrated in FIG. 3, the contact arm 20will remain in a normally open position until the lever 34 reaches anover center position. This over center position is a position whereinthe lever 34 has passed pivot point 31. Until approximately that pointof movement of the lever arm 34, spring link 39 expands and preloads thetoggle mechanism. When the lever 34 reaches its over center position thespring link causes the toggle to actuate at a rapid rate throwing thecontact arm from a position illustrated in FIG. 2 to that illustrated inFIG. 3.

While the circuit breaker mechanism 14 has been described in schematicterms, it should be understood that elaborations of these constructionsare contemplated and in fact are available in commercially manufacturedstructures at this time.

A more detailed arrangement of an actual commercially avialable circuitmechanism is illustrated in FIG. 1. As illustrated, such additionalfeatures as a De-ion arc quencher 44 may be used. This De-ion arcquencher consists of parallel steel plates partially surrounding thecontacts and enclosed by a fibre wrapper or ceramic support. Thisquencher is used to draw the are from the contacts into the plates asthe contacts .are open or closed. These plates function to disperse thearcs and reduce heat, thereby rapidly removing ions from the arc andimproving the build-up-time of the dielectric between the contacts. Inaddition, constructions are available in which double toggles and springlinks are used for more rapid actuation. However, in each of thepreferred embodiments it is important to use a circuit breaker embodyingthe over center spring actuated mechanism of the type herein described.

The preferred power supply is normally connected to the output or loadterminals 50, 51 and 52. Output or load terminal 50 is connected by busbars 53 and 54 respectively to circuit breakers 13 and 16. Load terminal51 is connected respecively by bus bars 55 and 57 to circuit breakers 14and 17, while load terminal 52 is connected by bus bars 58 and 59respectively to circuit breakers 15 and 18.

Each of the circuit breakers in each of the respective groups are tiedto the other circuit breakers in their group by suitable means forsynchronous operation. Such means may comprise a cross tie bar 66), 61,which may be suitably mounted by brackets to the contact arms 20. Thuseach contact arm 20 in the first group of circuit breakers .13, 14 and15 are actuated simultaneously by cross tie bar 60, and circuit breakers16, 17 and 18 in the second group are simultaneously actuated by bar 61.

The first group of circuit breakers 13, 14 and 15 are mechanicallyinterlocked to the second group circuit breakers 16, 17 and 18 so thatthey work in opposition. That is, when the first group of circuitbreakers 13, 14 and 15 are opened thereby disconnecting the load fromthe preferred power source, the second group of circuit breakers 16, 17and 18 are closing, and thereby connecting the load to the secondary oremergency power supply. These two groups of circuit breakers aremechanically interlocked by at least one tie rod 70. The tie rod 7'0 ispivotally interengaged at its ends 71 and 72 with rigid projections 74and 75 fixed respectively to the arms 20 of a circuit breaker in eachgroup. In a preferred embodiment of a three-pole transfer mechanism,mechanical interlocks or tie rods 70 are provided on each of the outerpair of circuit breakers in the group of three. It has been found thatthis symmetrical arrangement of the interlocking tie rods provides animproved and more balanced arrangement.

The first and second groups of circuit breakers are automaticallyoperated by means of a motor mechanism generally illustrated at 80. Thismechanism has a shaft 31 rotatable in one direction which shaft carriesa crank 82. The end of crank 82 has the connecting rods 83 and 84pivotably secured to it. The other endof the connecting rod 83 ispivotably connected to lever 3.4 of the circuit breaker 14, While theother end of the connecting rod 84 is pivotably connected at 87 to thelever 34 of the circuit breaker 17. As illustrated in this preferredembodiment the connecting rods in a double throw three pole system aresymmetrical with respect to the rods 70. They also function in part as amechanical interlock.

The motor preferably comprises a unidirectional high torque motor havinga single speed reduction, means which may comprise a worm and geararrangement 86, 87, with the worm coupled directly to the crank shaft ofthe motor and the gear to the crank arm. The motor also has a pair oflimit switches 90, 91 incorporated into its housing to permitincremental successive rotations of 1-80" with the motor powercontrolled by these switches.

Referring now to the mechanical arrangement of FIGS. 2 and 3, the motormechanism 80 is actuated incrementally to cause the crankarm 82 to move180 on each actuation. Thus, the crank arm 82 moves from a positionwherein its end 82a (FIG. 2) will move from one stable position shown inFIG. 2 to a position'180" out of the phase with that position shown inFIG. 2. When actuated the motor will cause the links 83 and 84 to pivotthe levers 34 on the opposite circuit breakers. Because the circuitbreakers of each group are tied together, all levers 34 in each groupwill move simultaneously. ,Because of the spring links 39, the crank 82will move over an angle of 90 during which time the toggle mechanism 28will remain stationary. However, during this time, the spring links 39preload the toggle mechanism so that when the crank is rotated to justbeyond 90, the levers 34 assume an over center position and the kineticenergy in the spring links 39 cause a rapid change over of the contactarms 20 from one stable position such as shown in FIG. 2 to the otherstable position shown in FIG. 3. By proper selection of the spring links39 and other parameters, the switch-oversgenerated by the kinetic energyof the springs will cause the contact arms to close more rapidly thanpossible under the influence of the motor 80. In the switched positionthe toggle mechanismpositively locks the closed contact such asillustrated in FIG. 3 at the right with a knee locking action.

One limit switch 91 controls the normal position and the other switch 90controls the emergencyposition. The switches are operatively mounted onand controlled by the motor shaft. To transfer from a normal loadcondition as illustrated in FIG. 4 to an emergency position the motor 80is actuated to rotate its shaft 180. This occurs when there is a failureor partial failure of power from the normal source. When this occurspower in the normal power lines 93, 94, drops. Thisdeenergizes coil 95of the normal power control relay A causing contacts 96 to open and 97to close. Emergency power control relay G is also closed if theemergency power source is high enough above a selected minimum level, asfor example 90%, to maintain coil 98 energized. Under these conditionsenergy will pass through lines 99, contacts 98, .line 100, contact 97and line 101 to terminals 3 of the motor. Since limit switch 91 isnormally closed the motor will actuate through when the motor itselfopens switch 91 and closes switch 90.

When the power in the normal circuit returns, coil95 is reenergizedcausing contacts 96 to close and contacts 97 to open. When contacts 97open the motor cannot be energized through motor contact 3 regardless ofthe condition of switch 91. However switch 90 which is now closedpermits power to pass to the motor through motor contact 1, line 105,contact 96 and 93 on reestablishment of normal power. This causes themotor 80 to rotate a second 180 until switch 90 is opened and switch 91is closed.

As previously indicated the main switch contacts are connected to theoperating mechanism through a spring loaded device that preloads throughthe first 90 degrees of travel and then allows the main contacts totransfer at high speed ahead of the motor operated mechanism. Ifby'chance, the motor is jogged to a position just beyond 90 degrees,sufiicient to transfer the circuit breaker but not suificient to operatethe limit switch, and if the power from the source to which the circuitbreaker has just transferred fails, the mechanism would assume a neutralposition electrically and could not be transferred to the other positionuntil the limit switch contacts have transferred. To prevent this anelectrical interlock circuit is provided with auxiliary contacts 110,111 connected to the bars 60, 61 of the circuit breakers with switch 110normally open and switch 111 normally closed to indicate the position ofthe circuit breaker main contacts. With the limit switch contacts insuch a neutral position after the circuit breakers have transferred, inorder to retransfer the first position, the motor mechanism is energizedthrough the control relay (A) and through the electrical interlockcontacts 110 and 111 to complete the previous cycle and then allow fortransfer in the other direction if power is available from that othersource.

What is claimed is:

1. In a transfer mechanism for transferring a load between first andsecond power supplies,

first and second switch mechanisms respectively operable to connect anddisconnect a load to and from said first and second supplies,

said switch mechanisms each having a toggle mecha nism connected to acontact arm and adapted to move said arm between an open position and aclosed position,

and also having a lever with a spring link between said lever and togglemechanism for snapping said arm from one of said positions to the other,

said lever and spring arranged to permit movement of said lever to adead center position before said toggle mechanism is actuated,

means rigidly interlocking said arms for simultaneous movement thereof,whereby only one of said arms may be closed at one time, and,

means operatively interengaging said levers for simultaneous opposedmovement of said contact arms whereby when one switch is opened theother is closed said means operatively interengaging said leverscomprising a crank arm with a pair of connecting links pivotablyconnected thereto with one of said links connected to one switchmechanism and the other link connected to the other switch mechanism,said crank arm constructed and arranged to rotate over an arc of 180 tocause each of said switch mechanism levers to pass through said deadcenter positions to actuate said toggle mechanisms.

2. A transfer switch mechanism for transferring a load from a first to asecond power supply comprising,

first and second switch mechanisms each having bistable conditions withfirst and second spring means for preloading said mechanisms withoutchanging said conditions and for coacting to change said conditions oncontinued loading beyond selected positions,

said first switch mechanism having a first contact arm and said secondswitch mechanism having a second contact arm,

6 a tie rod pivotably interconnected with said first and second contactarms for normally maintaining said arms in asymmetrical bistableconditions, and, means for synchronously actuating said first and second5 spring means to said selected positions at a first rate of speed whichis slower than the rate at which said spring means changes saidconditions beyond said selected positions. 3. A transfer switchmechanism for transferring a load 10 from a first to a second powersupply comprising,

first and second switch mechanisms each having bistable conditions withfirst and second spring means for preloading said mechanisms withoutchanging said conditions and for coacting to change said conditions oncontinued loading beyond selected positions,

a rigid tie rod pivotably interconnected with said first and secondswitch mechanisms for normally maintaining said mechanisms inasymmetrical bistable conditions, means for synchronously actuating saidfirst and second spring means to said selected positions at a first rateof speed which is slower than the rate at which said spring meanschanges said conditions beyond said selected positions,

said means for synchronously actuating said first and second springmeans comprising a unidirectional motor with limit switch means adaptedto deenergize said motor on rotation of its shaft over a preselected arcof rotation and after a time interval during which the bistableconditions of said switch mechanisms may be changed.

4. A switch mechanism as set forth in claim 2 wherein three pairs ofswitch mechanisms are provided and said pairs are symmetrically arrangedwith respect to said actuating means.

5. A transfer switch mechanism for transferring a load from a first to asecond power supply comprising,

first and second switch mechanisms each comprising a toggle meansconnected to a contact arm, said contact arms each having bistableconditions with first and second spring means for preloading said firstand second mechanisms without changing said arm conditions with saidspring means coacting to change said conditions on continued loadingbeyond selected positions,

a tie rod having its ends pivotally engaging respectively said first andsecond switch mechanism arms whereby said arms are maintained inasymmetrical bistable conditions, unidirectional motor means forsynchronously activating said first and second spring means to saidselected positions including a crank operated by said motor means andengaging a pair of longitudinally aligned connecting rods at adjacentends with the other ends of said rods respectively engaging differentswitch mechanisms at a pivotable lever of each mechanism,

said lever of each mechanism being connected to said toggle means ofeach mechanism by one of said spring means,

said motor means constructed and arranged to simultaneously move saidfirst and second spring means through said tie rods to an over centerposition of said first and second switch mechanisms at a first rate ofspeed with said spring means adapted to move said switch mechanism whenin said over center position at a second rate of speed in excess of saidfirst from one bistable to the other condition, said connecting rods andsaid tie rod providing a knee-locking action to lock said arms in theirbistable conditions.

6. A mechanism as set forth in claim 5 wherein three aligned pairs ofswitch mechanisms are provided.

7. A mechanism as set forth in claim 6 wherein said 75 connecting rodsare connected to the center pair of said switch mechanisms and said tierod is connected to one end pair of said switch mechanisms.

8. A mechanism as set -forth in claim 7 wherein a second tie-rod isconnected at its end to the other end pair of said switchmechanismswhereby said rods are symmetrically and parallelly arranged in respectto said connecting rods.

9. A transfer switchmechanism in accordance with claim and furthercomprising an electrical circuit with limit-switch means fordeenergizing'said motor means on-rotation of its shaft over apreselected arc of rotation after a time interval during which thebistable conditions of said switchmechanism are changed.

10. A transfer switch mechanism in accordance with claim 9 wherein saidelectrical circuit comprises means for sensing a partial failure of saidfirst power supply and for simultaneously actuating said motor meanstotransfer'from a first bistable condition to a second bistable conditionand for sensing reestablishment of said first power supply to actuatesaid motor means to return said switch mechanisms to said one bistablecondition. 11. A transfer switchmechanism in accordance with claim 10wherein said electrical circuit further-comprises 'means 'for preventingsaid mechanism from assuming an electrically neutral position.

References Cited by the Examiner UNITED STATES PATENTS 1,250,674 12/1917Scott ZOO- 50 2,807,684 9/1957 Ayers 0767 2,849,581 8/ 1958 Bingenheimer200-67 2,904,649 9/1959 Ranson 200 ROBERT K. SCHAEFER, Acting PrimaryExaminer. BERNARD A. GILHEANY, Examiner.

1. IN A TRANSFER MECHANISM FOR TRANSFERRING A LOAD BEBWEEN FIRST ANDSECOND POWER SUPPLIES, FIRST AND SECOND SWITCH MECHANISMS RESPECTIVELYOPERABLE TO CONNECT AND DISCONNECT A LOAD TO AND FROM SAID FIRST ANDSECOND SUPPLIES, SAID SWITCH MECHANISMS EACH HAVING A TOGGLE MECHANISMCONNECTED TO A CONTACT ARM AND ADAPTED TO MOVE SAID ARM BETWEEN AN OPENPOSITION AND A CLOSED POSITION, AND ALSO HAVING A LEVER WITH A SPRINGLINK BETWEEN SAID LEVER AND TOGGLE MECHANISM FOR SNAPPING SAID ARM FROMONE OF SAID POSITIONS TO THE OTHER, SAID LEVER AND SPRING ARRANGED TOPERMIT MOVEMENT OF SAID LEVER TO A DEAD CENTER POSITION BEFORE SAIDTOGGLE MECHANISM IS ACTUATED, MEANS RIGIDLY INTERLOCKING SAID ARMS FORSIMULTANEOUS MOVEMENT THEREOF, WHEREBY ONLY ONE OF SAID ARMS MAY BECLOSED AT ONE TIME, AND, MEANS OPERATIVELY INTERENGAGING SAID LEVERS FORSIMULTANEOUS OPPOSED MOVEMENT OF SAID CONTACT ARMS WHEREBY WHEN ONESWITCH IS OPENED THE OTHER IS CLOSED SAID MEANS OPERATIVELYINTERENGAGING SAID LEVERS COMPRISING A CRANK ARM WITH A PAIR OFCONNECTING LINKS PIVOTABLY CONNECTED THERETO WITH ONE OF SAID LINKSCONNECTED TO ONE SWITCH MECHANISM AND THE OTHER LINK CONNECTED TO THEOTHER SWITCH MECHANISM, SAID CRANK ARM CONSTRUCTED AND ARRANGED TOROTATE OVER AN ARC OF 180* TO CAUSE EACH OF SAID SWITCH MECHANISM LEVERSTO PASS THROUGH SAID DEAD CENTER POSITIONS TO ACTUATE SAID TOGGLEMECHANISMS.